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Exploratory Development of Theoretical Methods

The purpose of this FWP is to generate new theories, models, and algorithms that will be beneficial to the research programs at the Ames Laboratory and to the mission of DOE. This FWP will lead the development of theoretical tools to study a broad range of problems in physics, materials science, and chemical as well as biological systems. The generality of these tools allows the cross-fertilization of ideas from one problem to problems in an entirely different area through the common link of the mathematical formulation. Such leaps across topic areas and in some cases across disciplines are characteristic of the power of a fundamental physics-based approach to the development of new theoretical methods, facilitated by the availability of general theoretical tools applicable to very different sets of problems. Current efforts of this FWP includes (1) methods for accurate calculation of correlated electron systems; (2) methods for spin dynamics and quantum control of spin; and (3) methods for computational prediction and design of complex structures and materials.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Excited state of the solid-state emitter is shifted by random amount Δ from the desired position. The optical 180° control pulses are applied periodically, with a delay τ. In the rotating frame, each pulse swaps the ground and the excited state, reversing the detuning Δ → −Δ.

Much like being slightly off the frequency of a radio station destroys radio reception, the quality of light-emitting technologies has, until now, been severely limited by random fluctuations in the frequency of the emitted photons. Scientists demonstrated how this photon detuning can be suppressed using a series of short, controlled pulses applied to the emitter. The elegant solution is robust and applicable for many quantum systems, removing a major roadblock on the way to implementing large-scale quantum networks.

Extensive calculations revealed that the calcium-iridium-oxygen compound CaIrO3 is a Slater-type insulator, putting to rest the debate of whether the insulating nature of the metal oxide is Mott-type or Slater-type.

A newly-developed hybrid computational method has computed, for the first time, plutonium’s exotic crystal structure transformations and additionally calculated the volume-collapse transition of praseodymium. As plutonium is heated it undergoes six complex crystalline phase transitions—the most of any element at ambient pressure. Explaining these six different phases has been a long-standing challenge of solid-state physics. These calculations are the first theoretical description of all of the crystal phases of plutonium that agree with the experimental data.

We studied and implemented for the first time dynamical decoupling on a single solid-state spin, the spin of a nitrogen-vacancy (NV) center in diamond, and prolonged its coherence time by a factor of 25. Besides its fundamental importance, this achievement constitutes an important advance towards manipulating matter at the level of single spins and opens new possibilities for highly sensitive magnetic sensors, and possibly for qubits for larger scale quantum information processing.

We developed a global structure optimization method, genetic algorithm, for an efficient prediction of grain- boundary structures. Using this method, we predicted the most stable structures and a number of low-energy metastable structures for Si[001] symmetric tilted grain boundaries with various tilted angles. We show that most of the grain-boundary structures can be described by the structural unit model with the units being the dislocation cores and perfect-crystal fragments (see Fig. 1).